for reinforcements to occupy the hill was answered by Col. Strong Vincent, commanding the Third Brigade of the First Division of the Union V Corps. Vincent rapidly moved the four regiments of his brigade onto the hill, only ten minutes ahead of the approaching Confederates. Under heavy fire from Southern batteries, Vincent arranged his four regiments atop the hill with the 16th Michigan to the northwest, then proceeding counterclockwise with the 44th New York, the 83rd Pennsylvania, and finally, at the end of the line on the southern slope, the 20th Maine. With only minutes to spare, Vincent told his regiments to take cover and await the inevitable Confederate assault; he specifically ordered Col. Joshua L. Chamberlain, commanding the 20th Maine (at the extreme end of the Union line), to hold his position to the last man, at all costs. Were Chamberlain's regiment to be forced to retreat, the other regiments on the hill would be compelled to follow suit, and the entire left flank of Meade's army would be in serious jeopardy, possibly leading them to retreat and giving the Confederates their desperately needed victory at Gettysburg. The 15th Alabama attacks In their attack on Little Round Top, the 15th Alabama would be joined by the 4th and 47th Alabama Infantry, and also by the 4th and 5th Texas Infantry regiments. All of these units were thoroughly exhausted at the time of the assault, having marched in the July heat for over 20 miles (37 kilometers) prior to the actual attack. Furthermore, the canteens of the Southerners were empty, and Law's command to advance did not give them time to refill them. Approaching the Union line on the crest of the hill, Law's men were thrown back by the first Union volley and withdrew briefly to regroup. The 15th Alabama repositioned itself further to the right, attempting to find the Union left flank which, unbeknownst to it, was held by Chamberlain's 20th Maine. Chamberlain, meanwhile, had detached Company "B" of his regiment and elements of the 2nd U.S. Sharpshooters, ordering them to take a concealed position behind a stone wall 150 yards to his east, hoping to guard against a Confederate envelopment. Seeing the 15th Alabama shifting around his flank, Chamberlain ordered the remainder of his 385 men to form a single-file line. The 15th Alabama charged the Maine troops, only to be repulsed by furious rifle fire. Chamberlain